Selection of binding elements, such as antibodies, nucleic acid aptamers or peptide aptamers, in relatively short spans of time remains a key challenge, particularly with regard to fine tuning the selectivity, sensitivity and specificity for a desired target. Antibodies are valued for their high selectivity and affinity, however, they are also susceptible to degradation, aggregation, modification or denaturation. In addition, antibodies for therapeutic applications require production in mammalian cell lines; which is an expensive and complex process, having a probability of variation from batch to batch.
Engineered protein binders based on stable protein scaffolds have proved to be a successful strategy for production of affinity ligands since these ligands are smaller than antibodies, and are relatively stable and can be synthesized in microbial production systems. While many of these binders might be unsuitable for therapeutic applications because of their potential immunogenicity, they have found application as binders in analytical, diagnostics and chromatographic applications.
Binding-elements, such as aptamers are oligonucleotide affinity ligands that are selected for their high affinity binding to molecular targets. A variety of binding-elements have been developed based on nucleic acids, such as deoxyribonucleic acids (DNA), ribonucleic acids (RNA) or peptide nucleic acids (PNA). Discovery of oligonucleotide binders involves selection processes from a library of DNA, RNA or modified nucleic acid oligomers involving multiple cycles. An example of oligonucleotide binder selection is SELEX (systematic evolution of ligands by exponential enrichment), wherein multiple rounds of selection and amplification are carried out to develop binding-elements with the desired affinity and selectivity. Additionally, non-SELEX methods have also been developed for aptamer discovery, such as the NECEEM (non-equilibrium capillary electrophoresis of equilibrium mixtures) based method that relies on non-equilibrium capillary electrophoresis of equilibrium mixtures. While the SELEX approach is the most reliable and extensively used method for discovery of aptamers to date, SELEX method is labor-intensive, time-consuming and expensive. The NECEEM based method is less time consuming, however, the method is completely dependent on the use of a capillary electrophoresis instrument, sensitivity of the detector, size and charge of the target molecule.
Therefore, there is a need to develop an alternative approach for discovery of binding-elements having high affinity towards a variety of targets for a desired application in a short span of time.